This report described patients along with previous echocardiographic evidence indicate an association between aneurysm of the fossa ovale membrane of the atrial septum and prolapse of the mitral valve. The presence of aneurysm of a sinus of Valsalva and congenital anomalies of both aortic and pulmonic valves in 1 of the 2 patients suggests a developmental association of these additional anomalies with atrial septal aneurysm and MVP.